Hard carbon film and surface acoustic-wave substrate

Abstract

The invention offers a hard carbon film and a SAW substrate that are easy to fabricate or low in manufacturing cost while virtually maintaining the quality that affects the important properties of a device that comprises the hard carbon film or the SAW substrate. The hard carbon film comprises a composite film of graphite-like diamond and carbon clusters; the composite film has a continuous crystal structure.

What is claimed is:  
     
       1. A hard carbon film comprising a combined film of graphite-like diamond and carbon, wherein: 
       (1) a crystalline structure in said combined film is continuous such that interstices between grains of said graphite-like diamond are filled with said carbon clusters;  
       (2) the graphite-like diamond has a peak in the range of 1333 to 1335 cm −1  in Raman spectroscopy using an argon laser beam whose wavelength is 457.92 nm, and the peak has a FWHM of 6 cm −1  or more;  
       (3) the carbon clusters have only one peak in the range of 1500 to 1520 cm −1  in Raman spectroscopy using an argon laser beam whose wavelength is 457.92 nm, and the peak has a FWHM of 170cm −1  or less; and  
       (4) the hard carbon film has an Ic/Id ratio of 4 or more wherein the integrated intensity is Id when the peak by Raman spectroscopy for the graphite-like diamond, that is, the position P 1 =1333 to 1335cm −1 , at which the peak value exists, is integrated with respect to the range of P 1 +5cm −1 , and the integrated intensity is Ic when the peak by Raman spectroscopy for the carbon clusters, that is, the position P 2 =1500 to 1520 cm −1 , at which peak value exists, is integrated with respect to the range of P 2 +35cm −1 .  
     
     
       2. A hard carbon film as defined in  claim 1 , wherein the graphite-like diamond has an intensity ratio expressed as the ratio of I(111)/I(220) is 0.3 or less in X-ray diffraction wherein the integrated intensity is I(111) when the peak in plane (111) in X-ray diffraction for the graphite-like diamond, that is, the position P 3 =43 to 46°, at which the peak value exists, is integrated with respect to the range of P 3 ±1°, and the integrated intensity is I(220) when the peak in plane (220) in X-ray diffraction for the graphite-like diamond, that is, the position P 4 =73 to 76°, at which the peak value exists, is integrated with respect to the range of P 4 ±1. 
     
     
       3. A hard carbon film as defined in  claim 2 , wherein the graphite-like diamond has an intensity ratio expressed as the ratio of I(111)/I(220) ranging from 0.05 to 0.2 in X-ray-diffraction. 
     
     
       4. A hard carbon film as defined in  claim 1 , wherein the graphite-like diamond has a grain size of not more than 1.0 times the wavelength λ, used in SAW filters. 
     
     
       5. A hard carbon film as defined in  claim 1 , wherein the hard carbon film has a thermal conductivity of not less than 2 W/cmK and not more than 15 W/cmK. 
     
     
       6. A SAW substrate comprising at least: 
       a base metal  
       a hard carbon film as defined in  claim 1 , being amounted on the base material and  
       a piezoelectric film mounted on the hard carbon film.  
     
     
       7. A SAW substrate as defined in  claim 6 , wherein the piezoelectric film comprises a piezoelectric body selected from the group consisting of ZnO, LiNbO 3 , LiTaO 3 , and KNbO 3 . 
     
     
       8. A SAW substrate as defined in  claim 6 , wherein the base material comprises Si.